AbstractApplicationContext.getBean()通过prepareBeanFactory为注册的bean返回null

我想在spring应用程序上下文中动态定义MBeanServerConnection,所以我通过prepareBeanFactory()注册它的工厂。我可以看到bean存在于上下文中,但当我执行getBean()时,它会返回null!。

有什么建议吗?

    public static void main(String[] args) throws IOException, Exception, IntrospectionException, MalformedObjectNameException, ReflectionException {
    final AbstractApplicationContext context = new ClassPathXmlApplicationContext() {
        protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
            super.prepareBeanFactory(beanFactory);
            final MBeanServerConnectionFactoryBean clientConnection = new MBeanServerConnectionFactoryBean();
            try {
                clientConnection.setServiceUrl("service:jmx:jmxmp://" + "localhost:7777");
                beanFactory.registerSingleton("clientConn", clientConnection);
            } catch (MalformedURLException e) {

            }
        }
    };
    context.refresh();
    for (String name : context.getBeanNamesForType(Object.class)) {
        System.out.println(name);
    }
    MBeanServerConnection mb = context.getBean("clientConn", MBeanServerConnection.class);
    for (String s : mb.getDomains()) {
        System.out.println(s);
    }
}